The invention concerns a radio knife operating with high-frequency currents of approximately 4 MHz.
It is known that a radio knife is defined as an instrument used in surgery to cut tissues, comprising a generator of high-frequency current with intensity equal to a few hundred milliamperes provided with two electrodes, one of which is called plate, while the other, called handpiece, is active and has the shape of a needle, a small sphere or a bevelled blade. The patient on whom the radio knife must be used rests his/her body on the plate, while the radio knife is used for the operation. The cutting of the tissues is proportional to the intensity of the current passing between the electrodes and compared to the traditional knife with steel cutting blade this instrument offers the advantage of an almost complete hemostasis due to the coagulating action on the small vasa of the tissues and of a limited destruction of cells.
It is also known that the quantity of necrotized tissues produced during the cutting depends on the frequency of the generator current and tends to decrease as said frequency increases, said frequency being generally fixed in a few hundred kHz. A further increase in said frequency makes it necessary to use particular electronic components, such as vacuum tubes, makes the produced frequency unstable and requires high voltages in order to guarantee a constant cutting current. Furthermore, the use of vacuum tubes to generate high frequencies may prevent the necessary insulation of the circuit in which the cutting current flows from the surrounding environment, which does not ensure enough safety.
US 4,590,934 discloses a bipolar cutter/coagulator at the forceps of which there is waveform with the frequency of 1 MHz when the device operates as cutter. The waveform frequency varies between limits of 1 MHz plus or minus 4% when the device operates as coagulator.
The aim of the present invention is the implementation of a radio knife preferably operating with a 4 MHz frequency, so that no necrotic effect is produced on the cells adjacent to the cut according to the operating procedure described below.
Another aim of the invention is the implementation of a radio knife with standard solid components, which make it possible to employ limited voltages for the operation of the device and guarantee highly stable frequencies and the possibility of use for any type of operation, since the power delivered is independent of the load impedance.
The radio knife object of the invention should also ensure high safety levels and a cut with no necrotic effects on the adjacent cells, so that it is possible to use the equipment also on extremely delicate tissues (for example, the brain) and to use the local anaesthesia instead of the general anaesthesia, with obvious advantages for the recovery of the patient.
All the goals mentioned above and others that will be better highlighted below have been achieved through the implementation of a high-frequency radio knife that, according to the main claim, comprises a handpiece for the cut and a plate closing an electronic circuit, said circuit comprising:
a rectifier circuit fed by the mains voltage that supplies rectified pulsating voltage to a radiofrequency circuit;
a radiofrequency circuit capable of emitting an output current signal with a constant frequency of a few MHz, powering the radio knife by means of a radiofrequency transformer, and wherein said radio knife is characterized in that the radiofrequency circuit is obtained by piloting a MOSFET through a pilot circuit comprising a quartz-operated oscillator whose oscillation frequency amounts to at least twice the usual operating frequency of the MOSFET, said pilot circuit being controlled by a microprocessor current control circuit that takes a signal proportional to the current from a current sensor positioned after the MOSFET and is such as to maintain the radiofrequency circuit current limited to a value compatible with the power that can be dissipated by the MOSFET independently of any variation in the circuit load impedance, said impedance being constituted by the MOSFET stray capacitance, the radiofrequency transformer inductance and the impedance of the patient""s body part positioned between the radio knife and the circuit closing plate.
To advantage, according to the invention a 4 MHz frequency on the handpiece is used, with a substantially constant current independently of the load variation, which ensures a cut without necrosis; in fact, by properly proportioning the power the instantaneous evaporation of the intracellular liquids is obtained, thus taking heat from the cut area and preventing the spreading of said heat to the adjacent cells, which protects them against any damage.
It has been observed that 4 MHz is the optimal frequency, in fact a further increase in frequency would be detrimental, since the excessive reduction in the evaporation time would require a power increase that produces unwanted, damaging effects on the adjacent cell layers. It can therefore be concluded that the 4 MHz frequency represents the optimal operating value for a radio knife that does not produce any necrotic effect. This underlines also the importance of the stability of the operation frequency over time, independently of any variation in the power delivered and the load impedance that is constituted, as far as the current generator is concerned, by the tissues to be cut and can vary, according to the kind of operation, from a few dozen ohms to the kohm.
According to the application proposed by the invention, this result is achieved, as already explained, through the usexe2x80x94for the high-frequency oscillatorxe2x80x94of quartz-operated standard MOSFET adjusted by a current control device. The use of solid components to obtain high-frequency currents has considerable advantages compared to the use of vacuum tubes, due to the greater reliability of the former, to the lower voltages necessary for their operation and to their greater stability. However, there is a difficulty represented by the fact that the MOSFET operating with high frequency (radiofrequency MOSFET) can seldom support voltages exceeding 100 V, which are absolutely unsuitable for the application in question; on the other hand, the operating frequency of the MOSFET that are capable of supporting the 700-800 V required for the generator of a radio knife usually does not exceed 1 MHz.
The solution proposing the use of the circuit object of the invention makes it possible to employ standard MOSFET to obtain the high-frequency oscillator, though obtaining a 4 MHz current generator with voltages of approximately 700 V.
A further advantage is represented by the fact that the generator frequency is kept constant by means of a quartz-operated oscillator, while the current, in case of decrease in the load value, is automatically limited, in such a way as to guarantee the required power independently of the load impedance itself, that is, of the type of tissue and of operation. This is achieved by producing the required frequency with a quartz-operated oscillator that pilots the MOSFET operating in class C, since the resonant load is the result of the combination of the radiofrequency transformer inductance and of the stray capacitance of the MOSFET itself.
The current limitation is obtained on the MOSFET circuit through a hard-wired logic with quick comparators controlled by a microprocessor.
The solution object of the invention is also characterized by the fact that the current circuit is completely and galvanically insulated through the radiofrequency transformer (that is, the load is floating), in such a way as to make the equipment suitable for being operated together with other equipment (since it respects the current dispersion limits), thus making it impossible to operate the cutting current if not through the volume included between the plate and the handpiece, with evident advantages for the operators"" safety.